Effect of NusA protein on expression of the nusA,infB operon in E. coli.

Protein and operon fusions between lacZ and various genes of the nusA,infB operon have been constructed on lambda bacteriophages and used to show that the operon is negatively regulated by the level of NusA protein. Overproducing NusA (but not IF2) from a multicopy plasmid reduces the level of beta-galactosidase from the fusions indicating repression of the operon. Introducing the lambda carrying the fusions into nusA mutant strains produces a higher level of beta-galactosidase-indicative of derepression of the operon. In particular, a larger form of the NusA protein which does not affect bacterial growth per se causes a derepression of the operon. As both protein and operon fusions respond equivalently, we conclude that the nusA protein is acting at the transcriptional level to regulate expression of the nusA, infB operon.